In searching for an answer to this question I found a good summary on this site:
"Basil in The Garden
Most gardeners plant basil seeds directly into the garden bed (or in garden jargon, “in situ”) after the last frost date in their region has passed. As a native Mediterranean herb, basil likes to be planted in full sun (that’s 8 hours – or as close as you can get to it), and well-drained soil with some composted manure or other organic materials. Avoid over-watering the seedlings as basil is prone to “damping off” disease."
So, i looked up "damping off disease" and found the best layman's explanation on this site. With respect to the seeds which never emerged, it said this:
"Babies can be affected even before they break their seedcoat. Moisture from the fungus ridden soil enters into the seed and your plant is already doomed. In this case, you may not even have a seedling at all. It could rot under the soil before emerging. If you plant a ton of seeds and only get a few babies, then they probably fell to the fungus in the soil."
I am now extremely worried about the plants that DID emerge, but are not thriving - they may have root rot under the soil. Mr. Stripey, are you okay? Please sun, come back!
I may have to replant some of the lettuces, the peas, and definitely the basil.